TypeError: object is not a function (Node js)

Sorry but I have a question about Node.JS. I have to do a project about OAuth2 and I want to make a POST request.

exports.acceptedLog = function (req, res) {
request({
    method:'POST',
    uri:'https://10.10.121.94:3000/oauth/access?grant_type=password&username=sana&password=issam'
}, function (err, response, body) {

    if (err) {

        res.write(err);
        res.end();

    } else {

        console.log("there's no error");


        /*
        var token = JSON.parse(response.body);


        if (typeof(token.access_token) == "undefined") {
            res.redirect("https://10.10.121.94:3000/badAccess");
        } else {
            res.redirect('https://10.10.121.94:3000/protectedResource?accessToken=' + token.access_token);
        }
        */
    }
});

}

and in oauth2.js

exports.access = server.exchange(oauth2orize.exchange.password(function(username, password, scope, done) {
console.log("I'm here");


db.accessTokens.create(client, username, password, scope, function(err, accessToken) {
    if (err) {
        return done(err);
    }
    done(null, accessToken);
});

}));

Problem is that I have an error:

TypeError: object is not a function
    at callbacks (/Users/HammouAyoub/Documents/PinchProject/repo local/sample/oauth2orizev0.0.3/oauth2orize-master/examples/express2/node_modules/express/lib/router/index.js:272:11)
    at param (/Users/HammouAyoub/Documents/PinchProject/repo local/sample/oauth2orizev0.0.3/oauth2orize-master/examples/express2/node_modules/express/lib/router/index.js:246:11)
    at pass (/Users/HammouAyoub/Documents/PinchProject/repo local/sample/oauth2orizev0.0.3/oauth2orize-master/examples/express2/node_modules/express/lib/router/index.js:253:5)
    at Router._dispatch (/Users/HammouAyoub/Documents/PinchProject/repo local/sample/oauth2orizev0.0.3/oauth2orize-master/examples/express2/node_modules/express/lib/router/index.js:280:5)
    at Object.middleware [as handle] (/Users/HammouAyoub/Documents/PinchProject/repo local/sample/oauth2orizev0.0.3/oauth2orize-master/examples/express2/node_modules/express/lib/router/index.js:45:10)
    at Context.next (/Users/HammouAyoub/Documents/PinchProject/repo local/sample/oauth2orizev0.0.3/oauth2orize-master/examples/express2/node_modules/express/node_modules/connect/lib/http.js:204:15)
    at Context.actions.pass (/Users/HammouAyoub/Documents/PinchProject/repo local/sample/oauth2orizev0.0.3/oauth2orize-master/examples/express2/node_modules/passport/lib/passport/context/http/actions.js:77:8)
    at SessionStrategy.authenticate (/Users/HammouAyoub/Documents/PinchProject/repo local/sample/oauth2orizev0.0.3/oauth2orize-master/examples/express2/node_modules/passport/lib/passport/strategies/session.js:52:10)
    at attempt (/Users/HammouAyoub/Documents/PinchProject/repo local/sample/oauth2orizev0.0.3/oauth2orize-master/examples/express2/node_modules/passport/lib/passport/middleware/authenticate.js:246:16)
    at Passport.authenticate (/Users/HammouAyoub/Documents/PinchProject/repo local/sample/oauth2orizev0.0.3/oauth2orize-master/examples/express2/node_modules/passport/lib/passport/middleware/authenticate.js:247:7)

I really don't understand. And if I do a console.log in method(oauth2orize.exchange.password(function(username, password, scope, done)

I have nothing, can you help me please ?